In this modern age of digital photography, lens filters are often regarded as redundant, because many of the special effects can be replicated in post processing with software like photoshop. Traditionally we would use an ND Gradient filter to darken a sky, and allow us proper exposure of the ground. Now it is a piece of cake to blend two exposures, one for the sky, one for the ground, into one photo. The biggest drawback for the ND Grad filter is that unless you are shooting over flat ground, or the ocean, you will darken your hills, trees, buildings, or whatever. With photoshop this is easily avoided. ND Grads are still a far better option if you want to do long exposures though.
Filters that provide a tint, well thats easy too.
Digital cameras are not sensitive to UV light so a UV filter does nothing, but they do provide cheap protection for your lens’s front element. Better to damage a cheap filter than your lens.
But one filter that really can not be replicated is the Polarizer filter. If your camera is an auto focus one, you will need a Circular Polarizer or else the AF will not work. Most commonly they are a screw on filter. The filter screws onto the lens and then can spin, so you can adjust the angle of the polarization against the sunlight. If the filter is 90 degrees off it will have no polarization effect (though it will still knock about 1.5 stops of light out, which can also be handy). When you turn the filter around you will see the magic happen.
When using the filter, you just turn it until it looks good. Note it will really work best in bright sunlight or with a direct light source, it has less effect on a cloudy day.
Firstly the filter will reduce haze, increase contrast and the saturation of colours. Greens of trees will be enhanced, and it will really bring up and darken the blue of the sky, which can often appear pale and washed out. Compare these two photos…
This shot has EXACTLY the same shutter speed, aperture, ISO, focal length, white balance and colour profile setting, but the polarizer was turned around to effect…
But wait, theres more. As well as enhancing colour, the Circular Polarizer will also help get rid of or reduce reflections from non metallic objects. It will get rid of glare and reflections from water, windows, and its even good at getting rid of reflections in the paintwork of cars, though since they have complex shapes you may need to blend multiple exposures with different polarizer settings to get a great effect.
Check out these quick demo shots I took some time ago in Liverpool St, Hobart. Excuse the ordinary pictures, they are just snaps to be used for example…
Firstly without polarization..
Now THAT is something you simply can not do in Photoshop.
I also use the Circular Polarizer Filter a lot when shooting motorsport, as it allows me to slow down my shutter speed a bit to get a better motion blur in the background when panning, and you can also tweak the polarization to remove the glare from the car windows, so you can see inside the car, and of course the driver.
Circular Polarizers are expensive. Very expensive. My 82mm filter for my ultra wide angle lens nearly required the sale of some internal organs, but they are a very worthwhile investment, and really are an essential part of anyones gear bag if into landscape, architectural, or automotive photography.